The present invention relates to a color image forming apparatus using the electrophotography, and, more particularly, to a color image forming apparatus constructed such that a cleaning device together with an image retainer are mounted detachably on an apparatus body.
In order to form color images by the electrophotography, there have been proposed a number of methods and apparatus. In one of these methods, as disclosed in Japanese Patent Laid-Open No. 61-100770, for example, a color copy is obtained by forming and developing latent images according to the separated color number of a document image on an image retainer such as a photosensitive drum, by transferring each image developed to a transfer drum to form a multi-color image on the transfer drum and further transferring it to a recording paper. The apparatus using this method is required to have a transfer drum having such a size as to allow one image to be transferred to its circumference in addition to the photosensitive drum. As a result, the apparatus cannot be freed from a large size and a complicated structure.
As disclosed in Japanese Patent Laid-Open No. 61-149972, on the other hand, there is another method for forming a multi-color copy by forming and developing latent images according to a separated color number of a document image on a photosensitive drum and by transferring the images upon the individual developments to a transfer material. However, this method finds it difficult to overlap the multi-color images accurately so that an excellent color copy cannot be obtained.
There is still another method for forming a color image by repeating both formations of latent images according to a separated color number of a document image on a photosensitive drum and developments of the same with color toners for superposing the color toner images on the photosensitive drum and then transferring the same. The fundamental process of this multi-color image formations is disclosed in Japanese Patent Laid-Open Nos. 60-75850, 60-76766, 60-95456, 60-95458 or 60-158475.
In this multi-color image forming apparatus for forming a color image by such superposition, the photosensitive drum is surrounded around its circumferential edge by a plurality of developing devices which are stored with color toners of different colors. Generally speaking, the photosensitive drum is turned several times to develop the latent images thereon thereby to form a color image.
For the existing reproducing machine, on the other hand, there has been a proposal in which a photosensitive drum, a developing device and a cleaning device are mounted altogether on a support member to facilitate the replacements and remedies of the individual units, as disclosed in Japanese Patent Laid-Open No. 58-54392. For the monochromatic image, on the other hand, those devices are made integral and disposable to facilitate their replacements, as disclosed in Japanese Patent Laid-Open No. 57-154255. For the disposable cartridges for color images, moreover, there is disclosed in Japanese Patent Laid-Open No. 58-72159 a color cartridge which has a plurality of built-in developing devices to be disposed integrally.
No matter what structure might be taken, however, the multi-color image forming apparatus for forming a color image by superposing toner images of different colors while the photosensitive drum is rotated plural turns cannot be constructed such that the individual cleaning members (such as blade) composing the cleaning device are forced to contact with the photosensitive drum surface at all times, but requires a function to bring the cleaning members apart from the photosensitive drum surface, when the toner images are superposed. If, more specifically, the cleaning members (especially, blade) are always held in abutting contact with the photosensitive drum, the following troubles will occur:
(1) The photosensitive drum is deformed to have its photosensitive characteristics changed; PA1 (2) The cleaning member (blade) and the photosensitive drum are attached with the toners; and PA1 (3) The cleaning member is formed (For example, the cleaning blade is deformed to have its abutting pressure changed, or the fur brush itself is deformed).
A device for bringing the cleaning members into and out of contact with the drum surface is advisably disposed at the side of the body of the image forming apparatus rather than the side of the cleaning device because of mechanical and electrical connections between the body of the image forming apparatus and the cleaning device.
In such construction, however, the cleaning member is supported only by the supporting member and becomes unstable when the cleaning device is taken out from the body of the image forming apparatus, because the cleaning device has no device for bringing the cleaning member into and out of contact with the drum surface.
This raises a problem that the toners on the cleaning members drop from the clearance between the cleaning members and the drum, when the aforementioned process unit wherein the photosensitive drum is integrated with the cleaning device is to be taken out from the apparatus body, to blot the inside of the apparatus body and the surface of the floor. Another problem is that the photosensitive drum itself is seriously instable when it is disengaged from the apparatus body.